The present invention relates to a process and apparatus for treating heavy oil with supercritical water or subcritical water, thereby reforming heavy oil into light oil. More particularly, the present invention relates to a process and apparatus for removing vanadium contained in heavy oil at the time of heavy oil reformation. The present invention relates also to a power generation system which uses heavy oil as fuel for gas turbines.
It has been common practice to drive gas turbines in thermal electric power plants by burning gaseous fuel (such as LNG) or light oil (such as gas oil and kerosene). Gas turbines that run on heavy oil are shunned because they are subject to high temperature corrosion by vanadium contained in heavy oil; therefore, most gas turbines in practical use run on light oil. One way to cope with this situation is to incorporate heavy oil with magnesium as an additive which forms a high-melting composite oxide of magnesium and vanadium, thereby solidifying vanadium in the turbine. (See, for example, “Heavy oil combustion gas turbine”, by Nishijima, Journal of Gas Turbine Society of Japan, 11-43, 1983.) The problem involved with this method is that the high-melting composite oxide of magnesium and vanadium (which is called “ash”) sticks to turbine blades, making it necessary to suspend operation for blade cleaning. If vanadium is removed while heavy oil is being reformed into gas turbine fuel, then it would be possible to drive gas turbines economically at a low fuel cost.
Reformation of heavy oil into gas turbine fuel is accomplished by use of supercritical water which decomposes and cracks hydrocarbons in heavy oil, thereby yielding combustible gas. Reaction of heavy oil with supercritical water and alkali is also known as a means to remove sulfur components from heavy oil. Processes for reforming heavy oil with supercritical water or subcritical water are disclosed in Japanese Patent Laid-open Nos. 6-279763, 10-310780, 11-80750, 11-166183, 11-246876, 2000-109850, 2000-109851, and 2001-50010.
The prior art techniques mentioned above disclose nothing about the treatment of vanadium contained in heavy oil. If vanadium is removed from heavy oil before heavy oil is introduced into the gas turbine combustor, then it would be unnecessary to solidify vanadium after combustion and hence it would be unnecessary to suspend operation for blade cleaning.